[Update on 2013-06-22: I should've mentioned this a while ago, but the issue and patch I submitted were accepted and built into ReportGenerator 184.108.40.206, so if you have anything newer, you should be good.]
Recently I was working on a project at the Day Job, using OpenCover 220.127.116.11 and ReportGenerator 4.0.804 to report my test coverage, as is my wont, when the report generation started taking figuratively forever. Investigating, I saw something like
found report files: D:/sandbox/project/src/buildlogs/temp_test_coverage/Project.UnitTest.coverage.xml Loading report 'D:\sandbox\project\src\buildlogs\temp_test_coverage\Project.UnitTest.coverage.xml' Preprocessing report Indexing classes in directory 'D:\sandbox\project\src\Module1\SubPath\' Added coverage information of 370/370 auto properties to module 'Module1' Indexing classes in directory 'D:\'
My D: drive isn't the hugest, but it's big enough, so that explained the delay. And of course, I certainly didn't want anything above D:\sandbox\project\src indexed.
I took a peek at my .coverage.xml file and the ReportGenerator code and until I found the offending lines
<Module dhash="9A-A3-0A-C0-1D-57-BA-2A-C2-D4-5B-9E-08-DE-BD-2D-46-04-AF-32"> <FullName>D:\Sandbox\project\src\Module\UnitTest\bin\Release\Module.dll</FullName> <ModuleName>Module</ModuleName> <Files> … <File uid="803" fullPath="D:\sandbox\project\src\Module\File1.cs" /> <File uid="806" fullPath="D:\Sandbox\project\src\Module\File2.cs" /> <File uid="808" fullPath="D:\sandbox\project\src\Module\File3.cs" /> …
Note the "Latin capital letter S" at the beginning of "Sandbox" on the line with uid 806. All the other lines had a "Latin small letter S". When ReportGenerator goes looking for *.cs files to scan, it starts at the directory whose name is the longest common prefix of all the fullPaths. Because "S" isn't "s", it came up with "D:\".
I submitted an issue on the ReportGenerator CodePlex project, so maybe we'll see a fix soon.
Of course I wondered "Why does the S differ for that entry?" but I figured I'd look at one thing at a time, and locating the fix for ReportGenerator was quicker.